A 33-year-old motor boat owner spilled some fuel on the boat while the boat was docked and tried to vacuum it up, Seattle Fire Department spokesman Kyle Moore said. Investigators determined an electrical spark from the shop vacuum ignited gasoline vapors, causing a “flash fire” that burned the man.

The man jumped into the water and his girlfriend, uninjured, jumped in with him.

The 33-foot boat sustained damage to the interior of the cockpit, Moore said. Investigators estimate the incident caused $55,000 in damage.

The man suffered burns to his hands, arms, torso, face and neck. He was taken to the hospital in serious condition.